In recent years, it is general to hierarchically superpose similar functions to a network and to use functions of each hierarchy.
In a detailed example, a communication failure recovery function is provided to each of a plurality of superposed hierarchies (also called layers) such as IP (Internet Protocol), MPLS (Multi Protocol Label Switching), and Ethernet (a registered trademark). Furthermore, when a communication failure has occurred on a path, each layer detects the failure by its own communication failure recovery function.
Herein, in such a multi-layer network, there is a tendency that a failure detection time and failure recovery are shorter in a lower layer and the failure detection time and the failure recovery become longer in an upper layer. The general reason for this is because a communication section is shorter and a connection with physical resources is stronger in the lower layer than the upper layer, so that it is possible to expect high speed communication failure detection and failure recovery in the lower layer than the upper layer.
Therefore, it is general to use a policy that the upper layer expects failure recovery in the lower layer and waits without performing communication failure detection at the shortest time for which communication failure is detectable, and an upper network is stably held as much as possible.
However, since a time for expecting and waiting the operation of the lower layer is at least longer than a time until the lower layer actually detects the failure and recovers the failure, a certain degree of margin should be included. Accordingly, the failure detection time of the upper layer is set to be significantly longer than the shortest time for which an actual operation is possible.
On the other hand, as a network structure is complicated, it is necessary to provide a scheme of abstracting the network structure and comprehensively controlling an entire network.
As such a scheme, there has been considered a scheme using a technology such as GMPLS (Generalized Multi-Protocol Label Switching).
Particularly, in recent years, there has been considered a scheme of comprehensively and intensively controlling a network by a technology such as OpenFlow being standardized by ONF (Open Networking Foundation) which is an industrial organization. Since the version of the OpenFlow is continuously updated and a control range is expanded according to the version-up, network integration is also considered. Furthermore, cooperation control and the like of a communication failure recovery scheme are also expected in the future.
An example of the technology related to such GMPLS is disclosed in PTL 1. In PTL 1, it is pointed out that, when a failure occurs, a lower network of a multi-layer network can quickly take failure recovery measures such as setting a route for making a detour around the failure place, but that it is not possible to recognize execution situations of the failure recovery measures in such a lower network from a router. Therefore, the router needs to perform update of topology information and setting of a bypass route twice, that is, at the time of occurrence of failure and at the time of failure recovery in the lower network, resulting in an increase in a processing load.
Accordingly, in the technology disclosed in PTL 1, the router serving as an upper node does not update the topology information immediately at the time of the occurrence of the failure in the lower network but holds the update of the topology information for a predetermined time in expectation for a quick recovery of the lower network, thereby avoiding invalid route calculation.